A projection objective is commonly used in the field of lithographic, in particular microlithographic production of semiconductors, during which an object provided with a structure, which is also denoted as a reticle, is imaged using the projection objective onto a substrate which is denoted as a wafer. The object provided with the structure is typically arranged in an object plane of the projection objective, and the substrate (wafer) is arranged in an image plane of the projection objective. The substrate is often provided with a photosensitive layer upon the exposure of which via light through the projection objective the structure of the object is transferred onto the photosensitive layer. The desired structure can arise on the substrate after development of the photosensitive layer, the exposure operation being multiply repeated, depending on circumstances.
Various designs of projection objectives are known and include dioptric projection objectives (refractive elements and no reflective elements), catoptric projection objectives (reflective elements and no refractive elements) and catadioptric projection objectives (refractive elements and reflective elements).